Collaboratively locating disconnected clients and rogue access points in a wireless network

ABSTRACT

Methods are described for using collaboration of neighboring wireless devices to enable location of disconnected wireless devices and rogue wireless access points. A central server computes the locations of the neighboring clients and uses those locations to estimate the location of a disconnected client. These techniques may take advantage of the beaconing and probing mechanisms of IEEE 802.11 to ensure that connected clients do not pay unnecessary overheads for detecting disconnected clients. Methods are also described for detecting and locating rogue devices by collaboratively collecting information from neighboring devices and comparing the information to a database.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/047,022, filed Jan. 31, 2005, and entitled “Collaboratively LocatingDisconnected Clients And Rogue Access Points In A Wireless Network”,which claims the benefit of U.S. Provisional Patent Application No.60/613,055 entitled, “System And Method For Diagnosing Faults InWireless Networks,” filed on Sep. 24, 2004. Each of these applicationsis hereby incorporated by reference in its entirety.

The present application is also related to co-pending application Ser.No. 11/047,189, entitled “Detecting And Diagnosing Performance ProblemsIn A Wireless Network Through Neighbor Collaboration,” and 11/047,190entitled “Using A Connected Wireless Computer As A Conduit For ADisconnected Wireless Computer,” both filed on Jan. 31, 2005. Each ofthese applications is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates generally to network operations, and moreparticularly, to locating disconnected or unauthorized devices inwireless networks.

BACKGROUND OF THE INVENTION

The convenience of wireless networking has led to a wide-scale adoptionof wireless networks (e.g., IEEE 802.11 networks). Corporations,universities, homes, and public places are deploying these networks at aremarkable rate. However, a significant number of “pain points” remainfor end-users and network administrators. Users experience a number ofproblems such as intermittent connectivity, poor performance, lack ofcoverage, and authentication failures. These problems occur due to avariety of reasons such as poor access point layout, devicemisconfiguration, hardware and software errors, the nature of thewireless medium (e.g., interference, propagation), and trafficcongestion. Users frequently complain about connectivity and performanceproblems, and network administrators are expected to diagnose theseproblems while managing corporate security and coverage. Their task isparticularly difficult due to the unreliable nature of the wirelessmedium and a lack of intelligent diagnostic tools for determining thecause of these problems.

For companies with a large deployment of IEEE 802.11 networks, there maybe several thousand Access Points (APs) spread over many buildings.Problems with the networks result in end-user frustration and loss ofproductivity for the corporation. Furthermore, resolution of eachend-user complaint results in additional support personnel costs to acompany's IT department; this cost can be several tens of dollars andthis does not include the cost due to the loss of end-user productivity.

Fault diagnostics in IEEE 802.11 infrastructure networks has notgarnered attention from the research community relative to other higherprofile areas of research in wireless networking. Several companiesattempt to offer diagnostic tools, but these products lack a number ofdesirable features. For example, they do not do a comprehensive job ofgathering and analyzing the data to establish the possible causes of aproblem. Furthermore, most products typically only gather data from theAPs and neglect the client-side view of the network. Some products thatmonitor the network from the client's perspective require hardwaresensors, which can be expensive to deploy and maintain. Also, currentsolutions do not typically provide any support for disconnected clients,even though these are the ones that need the most help.

BRIEF SUMMARY OF THE INVENTION

The problems outlined above may at least in part be addressed by asystem and method for detecting and diagnosing faults in wirelessnetworks as described herein.

The following presents a simplified summary of the disclosure in orderto provide a basic understanding to the reader. This summary is not anexhaustive or limiting overview of the disclosure. The summary is notprovided to identify key and, or critical elements of the invention,delineate the scope of the invention, or limit the scope of theinvention in any way. Its sole purpose is to present some of theconcepts disclosed in a simplified form, as an introduction to the moredetailed description that is presented later.

In one embodiment, the monitoring architecture described herein is usedfor locating client machines that have become disconnected from awireless network. In another embodiment, the architecture is used fordetecting rogue or unauthorized access points in enterprise wirelessnetworks.

In one embodiment, a computer-readable medium includingcomputer-executable instructions is provided for determining thelocation of a disconnected wireless computing device, the wirelesscomputing device being disconnected from an infrastructure network, thecomputer-executable instructions executing on one or more connectedwireless computing devices in the vicinity of the disconnected device,and performing the steps of receiving one or more beacon signals fromthe disconnected device, recording signal strength information about thedisconnected device according to the beacon signals, informing adiagnostic server that the disconnected device is not connected to theinfrastructure network, and transmitting the signal strength informationto the diagnostic server for estimating the location of the disconnecteddevice, wherein the beacon signals are sent by the disconnected devicein response to a determination that the device is not connected to theinfrastructure network.

In another embodiment, a computer-readable medium includingcomputer-executable instructions is provided for determining thelocation of a disconnected wireless computing device, the wirelesscomputing device being disconnected from an infrastructure network andin the vicinity of one or more wireless devices being connected to theinfrastructure network, the computer-executable instructions executingon a server, and performing the steps of receiving signal strengthinformation about the disconnected device from the one or more connecteddevices, computing estimates of the locations of the one or moreconnected devices; and approximating the location of the disconnecteddevice using the computed estimates and the received signal strengthinformation.

In still another embodiment, a method is provided for identifying arogue wireless access point in an infrastructure network, methodcomprising the steps of receiving information about a suspicious accesspoint, the information collected by one or more nearby wirelesscomputing devices or access points, comparing the information with anaccess point database, and identifying the suspicious access point asrogue if the information is inconsistent with the access point database.

BRIEF DESCRIPTION OF THE DRAWINGS

While the appended claims set forth the features of the presentinvention with particularity, the invention and its advantages are bestunderstood from the following detailed description taken in conjunctionwith the accompanying drawings, of which:

FIG. 1 is a simplified schematic illustrating an exemplary architectureof a computing, as used in accordance with an embodiment of theinvention;

FIG. 2 is a diagram illustrating an exemplary wireless network forlocating disconnected clients and rogue access points, in accordancewith an embodiment of the invention;

FIG. 3 is a flow diagram illustrating a method for locating disconnectedclients, in accordance with an embodiment of the invention;

FIG. 4 is a flow diagram illustrating a method for collaborativelyobtaining information on access points in a wireless network, inaccordance with an embodiment of the invention;

FIG. 5 is a flow diagram illustrating a method for determining if anaccess point is rogue, in accordance with an embodiment of theinvention; and

FIG. 6 is a schematic diagram of software components used for locatingdisconnected clients and rogue access points, in accordance with anembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The methods and systems to locate disconnected clients and detect rogueaccess points will now be described with respect to preferredembodiments; however, the methods and systems of the present inventionare not so limited. Moreover, the skilled artisan will readilyappreciate that the methods and systems described herein are merelyexemplary and that variations can be made without departing from thespirit and scope of the invention. After reviewing this description, itshould be apparent to those skilled in the art that the foregoing ismerely illustrative and not limiting, having been presented by way ofexample only. Numerous modifications and other illustrative embodimentsare within the scope of one of ordinary skill in the art and arecontemplated as falling within the scope of the invention. Inparticular, although many of the examples presented herein involvespecific combinations of method operations or system elements, it shouldbe understood that those operations and those elements may be combinedin other ways to accomplish the same objectives. Operations, elements,and features discussed only in connection with one embodiment are notintended to be excluded from a similar role in other embodiments.Moreover, use of ordinal terms such as “first” and “second” in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another or thetemporal order in which operations of a method are performed, but areused merely as labels to distinguish one claim element having a certainname from another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

Listed below are many of the problems that users and networkadministrators face when using and maintaining corporate wirelessnetworks.

Connectivity problems: End-users complain about inconsistent or a lackof network connectivity in certain areas of a building. Such “deadspots” or “RF holes” can occur due to a weak RF signal, lack of asignal, changing environmental conditions, or obstructions. Locating anRF hole automatically is critical for wireless administrators; they canthen resolve the problem by either relocating APs or increasing thedensity of APs in the problem area or by adjusting the power settings onnearby APs for better coverage.

Performance problems: This category includes all the situations where aclient observes degraded performance, e.g., low throughput or highlatency. There could be a number of reasons why the performance problemexists, e.g., traffic slow-down due to congestion, RF interference dueto a microwave oven or cordless phone, multi-path interference, largeco-channel interference due to poor network planning, or due to a poorlyconfigured client/AP. Performance problems can also occur as a result ofproblems in the non-wireless part of the network, e.g., due to a slowserver or proxy. It is therefore useful for the diagnostic tool to beable to determine whether the problem is in the wireless network orelsewhere. Furthermore, identifying the cause in the wireless part isimportant for allowing network administrators to better provision thesystem and improve the experience for end-users.

Network security: Large enterprises often use solutions such as IEEE802.1x to secure their networks. However, a nightmare scenario for ITmanagers occurs when employees unknowingly compromise the security ofthe network by connecting an unauthorized AP to an Ethernet tap of thecorporate network. The problem is commonly referred to as the “Rogue APProblem”. These Rogue APs are one of the most common and seriousbreaches of wireless network security. Due to the presence of such APs,external users are allowed access to resources on the corporate network;these users can leak information or cause other damage. Furthermore,Rogue APs can cause interference with other access points in thevicinity. Detecting Rogue APs in a large network via a manual process isexpensive and time consuming; thus, it is important to detect such APsproactively.

Authentication problems: According to the IT support group's logs, anumber of complaints are related to users' inability to authenticatethemselves to the network. In wireless networks secured by technologiessuch as IEEE 802.1x, authentication failures are typically due tomissing or expired certificates. Thus, detecting such authenticationproblems and helping clients to bootstrap with valid certificates isimportant. The present invention will be more completely understoodthrough the following detailed description, which should be read inconjunction with the attached drawings. In this description, likenumbers refer to similar elements within various embodiments of thepresent invention. Aspects of the invention are illustrated as beingimplemented in a suitable computing environment. Although not required,the invention will be described in the general context ofcomputer-executable instructions, such as procedures, being executed bya personal computer. Generally, procedures include program modules,routines, functions, programs, objects, components, data structures,etc. that perform particular tasks or implement particular abstract datatypes. Moreover, those skilled in the art will appreciate that theinvention may be practiced with other computer system configurations,including hand-held devices, multi-processor systems, microprocessorbased or programmable consumer electronics, network PCs, minicomputers,mainframe computers, and the like. The invention may also be practicedin distributed computing environments where tasks are performed byremote processing devices that are linked through a communicationsnetwork. In a distributed computing environment, program modules may belocated in both local and remote memory storage devices. The termcomputer system may be used to refer to a system of computers such asmay be found in a distributed computing environment.

FIG. 1 illustrates an example of a suitable computing system environment100 on which aspects of the invention may be implemented. The computingsystem environment 100 is only one example of a suitable computingenvironment and is not intended to suggest any limitation as to thescope of use or functionality of the invention. Neither should thecomputing environment 100 be interpreted as having any dependency orrequirement relating to any one or combination of components illustratedin the exemplary operating environment 100. Although one embodiment ofthe invention does include each component illustrated in the exemplaryoperating environment 100, another more typical embodiment of theinvention excludes non-essential components, for example, input/outputdevices other than those required for network communications.

With reference to FIG. 1, an exemplary system for implementing theinvention includes a general purpose computing device in the form of acomputer 110. Components of the computer 110 may include, but are notlimited to, a processing unit 120, a system memory 130, and a system bus121 that couples various system components including the system memoryto the processing unit 120. The system bus 121 may be any of severaltypes of bus structures including a memory bus or memory controller, aperipheral bus, and a local bus using any of a variety of busarchitectures. By way of example, and not limitation, such architecturesinclude Industry Standard Architecture (ISA) bus, Micro ChannelArchitecture (MCA) bus, Enhanced ISA (EISA) bus, Video ElectronicsStandards Association (VESA) local bus, and Peripheral ComponentInterconnect (PCI) bus also known as Mezzanine bus.

The computer 110 typically includes a variety of computer readablemedia. Computer readable media can be any available media that can beaccessed by the computer 110 and includes both volatile and nonvolatilemedia, and removable and non-removable media. By way of example, and notlimitation, computer readable media may comprise computer storage mediaand communication media. Computer storage media includes volatile andnonvolatile, removable and non-removable media implemented in any methodor technology for storage of information such as computer readableinstructions, data structures, program modules or other data. Computerstorage media includes, but is not limited to, RAM, ROM, EEPROM, flashmemory or other memory technology, CD-ROM, digital versatile disks (DVD)or other optical disk storage, magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices, or any othermedium which can be used to store the desired information and which canbe accessed by the computer 110. Communication media typically embodiescomputer readable instructions, data structures, program modules orother data in a modulated data signal such as a carrier wave or othertransport mechanism and includes any information delivery media. Theterm “modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, RF, infrared and otherwireless media. Combinations of the any of the above should also beincluded within the scope of computer readable media.

The system memory 130 includes computer storage media in the form ofvolatile and/or nonvolatile memory such as read only memory (ROM) 131and random access memory (RAM) 132. A basic input/output system 133(BIOS), containing the basic routines that help to transfer informationbetween elements within computer 110, such as during start-up, istypically stored in ROM 131. RAM 132 typically contains data and/orprogram modules that are immediately accessible to and/or presentlybeing operated on by processing unit 120. By way of example, and notlimitation, FIG. 1 illustrates operating system 134, applicationprograms 135, other program modules 136 and program data 137.

The computer 110 may also include other removable/non-removable,volatile/nonvolatile computer storage media. By way of example only,FIG. 1 illustrates a hard disk drive 141 that reads from or writes tonon-removable, nonvolatile magnetic media, a magnetic disk drive 151that reads from or writes to a removable, nonvolatile magnetic disk 152,and an optical disk drive 155 that reads from or writes to a removable,nonvolatile optical disk 156 such as a CD ROM or other optical media.Other removable/non-removable, volatile/nonvolatile computer storagemedia that can be used in the exemplary operating environment include,but are not limited to, magnetic tape cassettes, flash memory cards,digital versatile disks, digital video tape, solid state RAM, solidstate ROM, and the like. The hard disk drive 141 is typically connectedto the system bus 121 through a non-removable memory interface such asinterface 140, and magnetic disk drive 151 and optical disk drive 155are typically connected to the system bus 121 by a removable memoryinterface, such as interface 150.

The drives and their associated computer storage media, discussed aboveand illustrated in FIG. 1, provide storage of computer readableinstructions, data structures, program modules and other data for thecomputer 110. In FIG. 1, for example, hard disk drive 141 is illustratedas storing operating system 144, application programs 145, other programmodules 146 and program data 147. Note that these components can eitherbe the same as or different from operating system 134, applicationprograms 135, other program modules 136, and program data 137. Operatingsystem 144, application programs 145, other program modules 146, andprogram data 147 are given different numbers hereto illustrate that, ata minimum, they are different copies. A user may enter commands andinformation into the computer 110 through input devices such as atablet, or electronic digitizer, 164, a microphone 163, a keyboard 162and pointing device 161, commonly referred to as a mouse, trackball ortouch pad. Other input devices (not shown) may include a joystick, gamepad, satellite dish, scanner, or the like. These and other input devicesare often connected to the processing unit 120 through a user inputinterface 160 that is coupled to the system bus, but may be connected byother interface and bus structures, such as a parallel port, game portor a universal serial bus (USB). A monitor 191 or other type of displaydevice is also connected to the system bus 121 via an interface, such asa video interface 190. The monitor 191 may also be integrated with atouch-screen panel or the like. Note that the monitor and/or touchscreen panel can be physically coupled to a housing in which thecomputing device 110 is incorporated, such as in a tablet-type personalcomputer. In addition, computers such as the computing device 110 mayalso include other peripheral output devices such as speakers 197 andprinter 196, which may be connected through an output peripheralinterface 194 or the like.

The computer 110 may operate in a networked environment using logicalconnections to one or more remote computers, such as a remote computer180. The remote computer 180 may be a personal computer, a server, arouter, a network PC, a peer device or other common network node, andtypically includes many or all of the elements described above relativeto the computer 110, although only a memory storage device 181 has beenillustrated in FIG. 1. The logical connections depicted in FIG. 1include a local area network (LAN) 171 and a wide area network (WAN)173, but may also include other networks. Such networking environmentsare commonplace in offices, enterprise-wide computer networks, intranetsand the Internet.

When used in a LAN networking environment, the computer 110 is connectedto the LAN 171 through a network interface or adapter 170. When used ina WAN networking environment, the computer 110 typically includes amodem 172 or other means for establishing communications over the WAN173, such as the Internet. The modem 172, which may be internal orexternal, may be connected to the system bus 121 via the user inputinterface 160 or other appropriate mechanism. In a networkedenvironment, program modules depicted relative to the computer 110, orportions thereof, may be stored in the remote memory storage device. Byway of example, and not limitation, FIG. 1 illustrates remoteapplication programs 185 as residing on memory device 181. It will beappreciated that the network connections shown are exemplary and othermeans of establishing a communications link between the computers may beused. In particular, the computer 110 preferably contains a wirelessnetworking interface or wireless card, operating according to an IEEE802.11 protocol.

In an embodiment of the invention, a system consists of severalcomponents, as illustrated in FIG. 2. A Diagnostic Client (DC) 202 issoftware that runs on a wireless client machine 204. A Diagnostic AP(DAP) 206 runs on an Access Point 208. A Diagnostic Server (DS) 210 runson a backend server 212 of the organization.

In some embodiments of the invention, the Diagnostic Client module 202monitors the RF environment and the traffic flow from neighboringclients 214 and APs 216. During normal activity, the client's wirelesscard is not placed in promiscuous mode. The DC 202 uses the collecteddata to perform local fault diagnosis. Depending on the individualfault-detection mechanism, a summary of this data is transmitted to theDAPs 206 or DSs 210 at preferably regular intervals. In addition, the DC202 is programmed to accept commands from the DAP 206 or the DS 210 toperform on-demand data gathering, e.g., switching to promiscuous modeand analyzing a nearby client's performance problems. In case thewireless client 204 becomes disconnected, the DC 202 logs data to alocal database/file. This data can be analyzed by the DAP 206 or DS 210at some future time when network connectivity is resumed.

The Diagnostic AP 206 accepts diagnostic messages from DCs 202, mergesthem along with its own measurements and sends a summary report to theDS 210. Some embodiments of the invention do not include the DiagnosticAP 206. The DAP 206 offloads work from the DS 210. Some embodiments ofthe invention include a mixture of legacy APs 220 and DAPs 206: if an APis a legacy AP 220, its monitoring functions are performed by the DCs202 and its summarizing functions and checks are performed at the DS210.

The Diagnostic Server 210 accepts data from DCs 202 and DAPs 206 andperforms the appropriate analysis to detect and diagnose differentfaults. The DS 210 also has access to a database 221 that stores eachAP's 208 location. Network administrators can deploy multiple DSs 210 inthe system to balance the load, for example, by hashing each AP's MACaddress to a particular DS 210. In some embodiments, the DiagnosticServer 210 interacts with other network servers, such as a RADIUS 230and Kerberos 232 servers, to get client authorization and userinformation.

The exemplary system described with reference to FIG. 2 supports bothreactive and proactive monitoring. In proactive monitoring, DCs and DAPsmonitor the system continuously: if an anomaly is detected by a DC, DAP,or DS, an alarm is raised for a network administrator to investigate.The reactive monitoring mode is used when a support personnel wants todiagnose a user complaint. The personnel can issue a directive to aparticular DC from one of the DSes to collect and analyze the data fordiagnosing the problem.

The exemplary system imposes negligible overheads with respect to powermanagement. Both the proactive and reactive techniques described laterconsume very little bandwidth, CPU, or disk resources; as a result, theyhave negligible impact on battery consumption. The exemplary systemarchitecture shown in FIG. 2 supports several functions in embodimentsof the invention by using the DCs, DAPs and DSes. Some of the supportedfunctions include: locating disconnected clients; helping disconnectedclients; isolating performance problems; and detecting rogue accesspoints.

In some embodiments of the invention, the DAP 206 is a softwaremodification on AP 208, allowing for better scalability and foranalyzing an AP's performance. Since no hardware modifications arenecessary, the bar for deploying this embodiment is lower.

The client machines 204 and access points 208 preferably have theability to control beacons and probes. Additionally, client machines 204preferably have the capability of starting an infrastructure network(i.e., becoming an AP) or an ad hoc network (i.e., computer-to-computer)on their own; this ability is supported by many wireless cards currentlyavailable in the marketplace. Some embodiments of the invention make usethe presence of nearby clients or access points. By taking advantage ofnearby clients and access points instrumented with software “sensors”,deployment costs are potentially lowered.

The backend server 212 preferably uses a database to maintain thelocation of all the access points in the network. Such locationdatabases are preferably maintained by network administrators.

The exemplary system illustrated in FIG. 2 can scale with the number ofclients and APs in the system. The system contains two shared resources:DSs and DAPs. To prevent a single Diagnostic Server from becoming apotential bottleneck, additional DSs are preferably added as the systemload increases. Furthermore, some embodiments allow each individual DSto offload work by sharing the diagnosis burden with the DCs and theDAPs; the DS is used only when the DCs and DAPs are unable to diagnosethe problem and the analysis requires a global perspective andadditional data (e.g., signal strength information obtained frommultiple DAPs may be needed for locating a disconnected client).

Similarly, since the DAP is a shared resource, making it do extra workcan potentially hurt the performance of all its associated clients. Toreduce the load on a DAP, some embodiments of the invention use anoptimization technique, whereby an AP does not perform active scanningif any client is associated with it; the associated clients performthese operations as needed. The AP continues to perform passivemonitoring activities that have a negligible effect on its performance.If there is no client associated, the AP is idle and it can performthese monitoring operations. This approach ensures that most of thephysical area around the AP is monitored without hurting the AP'sperformance.

In one embodiment, the interactions between the DC, DAP, and DS aresecured using EAP-TLS certificates issued over IEEE 802.1x. Anauthorized certification authority (CA) issues certificates to DCs, DAPsand DSs; these certificates are used to ensure that all communicationbetween these entities is mutually authenticated. One embodimentincludes known techniques for detecting malicious behavior by legitimateusers.

The ability to locate disconnected wireless clients automatically in afault diagnosis system is potentially useful for proactively determiningproblematic regions in a deployment, e.g., poor coverage or highinterference (locating RF holes) or for locating possibly faulty APs. Inembodiments of the invention, a disconnected client determines that itis in an RF hole if it does not hear beacons from any AP (as opposed tobeing disconnected due to some other reason such as authenticationfailures). To approximately locate disconnected clients (and hence helpin locating RF holes), embodiments use a technique called DoubleIndirection for Approximating Location or DIAL, described with referenceto FIG. 3.

When a client 302 discovers that it is disconnected at step 304, itbecomes an AP or starts an ad hoc network and starts beaconing at step306. To determine the approximate location of this client, nearbyconnected clients 308 hear the client's 302 beacons at step 310 andrecord the signal strength (RSSI) of these packets at step 312. At step314, they inform the DS 316 that client 302 is disconnected and send thecollected RSSI data. The DS 316 then, at step 318, executes the firststep of DIAL to determine the location of the connected clients: thiscan be done using any known location-determination technique in theliterature, such as those described by P. Bahl and V. N. Padmanabhan in“RADAR: An Inbuilding RF-based User Location and Tracking System,” inProc. of IEEE INFOCOM, Tel-Aviv, Israel, March 2000, and by A. Ladd etal. in “Robotics-Based Location Sensing using Wireless Ethernet,” inProc. of ACM MobiCom, Atlanta, Ga., September 2002, which are herebyincorporated by reference in their entirety for all that they teachwithout exclusion of any part thereof. At step 320, the DS 316 uses thelocations of the connected clients as “anchor points” and thedisconnected client's RSSI data to estimate its approximate location.This step is preferably performed using any scheme that uses RSSI valuesfrom multiple clients for determining a machine's location, such asthose described in the references above or by any other known method.Since locating the connected clients results in some error, consequentlylocating disconnected clients with these anchor points can furtherincrease the error. However, it has been empirically shown that thiserror is approximately 10 to 12 meters which is acceptable forestimating the location of disconnected clients.

Turning to FIG. 4, a method of detecting rogue APs is discussed, inaccordance with an embodiment of the invention. Rogue APs areunauthorized APs that have been connected to an Ethernet tap in anenterprise or university network; such APs can result in security holes,and unwanted RF and network load. Rogue APs are considered a majorsecurity issue for enterprise wireless LANs. By using clients and (ifpossible) APs to monitor the environment around them, embodiments of theinvention detect rogue APs. The approach is to make clients and DAPscollect information about nearby access points and send it to the DS.When the DS receives information about an AP X, it checks an AP locationdatabase and ensures that X is a registered AP in the expected locationand channel. The approach detects rogue APs using off-the-shelf IEEE802.11-compliant hardware. This suffices to function as a low-costmechanism that addresses the common case Rogue AP problem being faced incurrent deployments: for many networks administrators, the main goal isto detect APs inadvertently installed by employees for experimentationor convenience. Other embodiments may implement detection ofnon-compliant Rogue access points and clients as well. If two companieshave neighboring wireless networks, the other companies' access pointsare preferably detected as Rogue APs. If this classification isunacceptable, the network administrators of the respective companies canshare their AP location databases.

Each DC 402 monitors the packets in its vicinity (in a nonpromiscuousmode), and for each AP 404 that it detects, it sends a 4-tuple <MACaddress, SSID, channel, RSSI> to the DS 406. Essentially, the 4-tupleuniquely identifies an AP in a particular location and channel. To getthis information, a DC 402 determines the MAC addresses of all APs 404around it.

The DC 402 can obtain the MAC address of an AP 404 by switching topromiscuous mode and observing data packets (it can use the FromDS andToDS bits in the packet to determine which address belongs to the AP).However, the same effect is preferably achieved using the followingapproach: since IEEE 802.11 requires all APs to broadcast beacons atregular intervals at step 408, the DC 402 listens for the beacons atstep 410 and obtains the MAC addresses from the APs' 404 beacons fromall the APs that it can hear at step 412. It has been shown that a DC402 not only hears beacons on its channel but it may also hear beaconsfrom overlapping channels as well; this property increases thelikelihood of a Rogue AP being detected.

To ensure that a Rogue AP does not go undetected, even if no client ispresent on any channel overlapping with the AP, embodiments use theActive Scanning mechanism of the IEEE 802.11 protocol: when a client 402(for example, a diagnostic client running on a wireless computer or onan access point) wants to find out what APs 404 are nearby, the client402 goes to each of the 11 channels (in 802.11b), and sends ProbeRequests at step 414. The client 402 waits for Probe Responses to besent from all APs at step 416 that hear those Probe Requests; from theseresponses, the DC obtains the APs' 404 MAC addresses at step 418. EveryIEEE 802.11-compliant AP must respond to such requests; in somechipsets, no controls are provided to disable this functionality. A BusyAP Optimization is preferably used so that active scans in an AP'svicinity are performed by an AP only when it has no client associatedwith it. In embodiments of the invention, Active Scanning is preferablyperformed on demand, for example, at the request of a networkadministrator as communicated through diagnostic clients and diagnosticaccess points. Alternatively, Active Scanning is performed regularly ona periodic basis or according to a policy set by a networkadministrator.

Once the client 402 has collected AP information, it sends the 4-tuplesto the DS 406 at step 420. The DS 406 then determines whether the AP isa rogue AP at step 422, described in more detail below.

Turning to FIG. 5, when the DS receives information for an AP fromvarious clients at step 502, it uses DIAL to estimate the AP'sapproximate location based on these clients' locations and the AP's RSSIvalues from them at step 504, using methods such as those describedabove with reference to FIG. 3. The DS classifies an AP as rogue if a4-tuple does not correspond to a known legal AP in the DS's AP locationdatabase at step 506, i.e., if the MAC address is not present in thedatabase, or if the AP is not in the expected location at step 508, orthe SSID does not correspond to the expected SSID(s) in the organizationat step 510. In some embodiments, if an AP's SSID corresponds to an SOSSSID, the DS skips further analysis since this AP may actuallycorrespond to a disconnected client that is executing a connection setupphase of a Client Conduit protocol, as described in co-pendingapplication entitled “USING A CONNECTED WIRELESS COMPUTER AS A CONDUITFOR A DISCONNECTED WIRELESS COMPUTER” by Adya, et al., filed Jan. 31,2005 with attorney docket number 231441. The channel information is usedin a slightly different way. As stated above, if an AP is on a certainchannel, it is possible to be heard on overlapping channels. Thus, an APis classified as rogue at step 512 only if it is reported on a channelthat does not overlap with the one on which it is expected. If thechannel on an AP is changed, the DAP preferably asks the DS to updateits AP location database (recall that the communication between the DAPand the DS is authenticated; if the AP is a legacy AP, the administratorcan update the AP location database when the AP's channel is changed).

A Rogue AP R might try to use MAC address spoofing to avoid beingdetected, i.e., send packets using the MAC address corresponding to areal AP G. However, the DS in embodiments of the invention still detectsR since R will reside in a different location or channel than G (if itis on the same channel and location, G immediately detects it). Notethat a Rogue AP is detected even if it does not broadcast the SSID inits beacons since a DC can still obtain the AP's MAC address from thebeacon. Such unauthorized APs are alternatively detected by disallowingAPs that do not broadcast SSIDs in an enterprise LAN.

In embodiments of the invention, an unauthorized AP may stay undetectedfor a short time by spoofing an existing AP X near X's location, beacona valid SSID in the organization, and stay on a channel on which no DCor AP can overhear its beacons. However, when a nearby client performsan active scan, the Rogue AP will be detected. To detect such rogue APs,a DC preferably performs such a scan every 5 minutes.

Turning attention to FIG. 6, details of one embodiment of animplementation are shown. The basic architecture consists of the DC, DAPand DS daemons running on clients, access points and servers,respectively. The system can be implemented, for example, on theMICROSOFT WINDOWS operating system with standard commercial 802.11bcards. On the DS, the daemon process accepts information from DAPs. TheDS reads the list of legitimate APs from a file or database. Thestructure of the code on the DC or DAP preferably comprises a user-leveldaemon 602 and kernel level drivers 604 and 606. These pieces arestructured such that code is added to the kernel drivers 604 and 606only if the functionality cannot be achieved in the user-level daemon602 or if the performance penalty is too high.

There are two kernel drivers in the exemplary system—a miniport driver604 and an intermediate driver (IM driver) 606, such as the Native WiFidriver in the MICROSOFT WINDOWS operating system. The miniport driver604 communicates directly with the hardware and provides basicfunctionalities such as sending/receiving packets, setting channels,etc. It exposes sufficient interfaces such that functions likeassociation, authentication, etc. can be handled in the IM driver 606.The IM driver 606 supports a number of interfaces (exposed via ioctls)for querying various parameters such as the current channel,transmission level, power management mode, SSID, etc. In addition toallowing the parameters to be set, it allows the user-level code torequest for active scans, associate with a particular SSID, capturepackets, etc. In general, it provides a significant amount offlexibility and control to the user-level code.

Even though many operations are already present in the IM driver 606,embodiments of the invention used modifications to expose certainfunctionalities and to improve performance of specific protocols. Theminiport driver 604 is preferably changed minimally to expose certaintypes of packets to the IM driver 606. In the IM driver 606, thefollowing support is preferably added: capturing packet headers andpackets; storing the RSSI values from received packets; keeping track ofAP information; and kernel event support for protocol efficiency. Thesemodifications are now discussed in further detail.

Capturing packet headers and packets: Embodiments of the invention allowfilters to be set such that only certain packets or packet headers arecaptured, e.g., filters based on specific MAC addresses, packet types,packet subtypes (such as management and beacon packets), etc.

Storing the RSSI values from received packets: Embodiments of theinvention obtain the RSSI value of every received packet and maintain atable called the NeighborInfo table that keeps track of the RSSI valuefrom each neighbor (indexed on the MAC address). An exponentiallyweighted average is maintained with the new value given some weightingfactor of, for example, 0.25. The RSSI information is preferably usedfor estimating the location of disconnected clients and APs using DIAL.

Keeping track of AP information: In the NeighborInfo table, embodimentskeep track of the channels on which packets were heard from a particularMAC address, SSID information (from beacons), and whether the device isan AP or a station. This information is preferably sent to the DAP/DSfor Rogue AP detection.

Kernel event support for protocol efficiency: An event is preferablyadded that is shared between the kernel and user-level code. The kerneltriggers this event when an “interesting” event occurs; this allows someof the protocols to be interrupt-driven rather being polling based.

Additionally, a number of ioctls are preferably added to get and clearthe information discussed above.

In embodiments of the invention, the diagnostics daemon 602 runs on adevice and gathers information and implements various mechanismsdiscussed above, e.g., collect MAC addresses of APs for Rogue APdetection, etc. If the device is an AP, it communicates diagnosticinformation with the DS and the DCs; if the device is just a DC, itcommunicates with its associated AP to convey the diagnosticinformation. The Diagnostic daemon on the DC obtains the currentNeighborInfo table from the kernel 608 at a periodic interval, forexample every 30 seconds. If any new node has been discovered or if theexisting data has changed significantly (e.g., RSSI value of a clienthas changed by more than a factor of 2), it is sent to the DAP. The DAPalso preferably maintains a similar table indexed on MAC addresses.However, it only sends information about disconnected clients and APs tothe DS; otherwise, the DS would end up getting updates for every clientin the system, making it less scalable. The DAP sends new or changedinformation about APs to the DS periodically (e.g., 30 seconds).Furthermore, if the DAP has any pending information about a disconnectedclient D, it informs the DS immediately so that the disconnected can beserviced in a timely fashion. All messages from the DC to the DAP andfrom DAP to the DS are preferably sent as XML messages. A sample messageformat from the DC is shown below (timestamps have been removed):<DiagPacket Type=“RSSIInfo” TStamp=“...”> <Clients TStamp=“...”><MacInfo MAC=“00:40:96:27:dd:cc” RSSI=“23” Channels =“19” SSID=“”TStamp=“...”/> </Clients> <Real-APs TStamp=“...”> <MacInfoMAC=“00:20:a6:4c:c7:85” RSSI=“89” Channels=“12” SSID=“UNIV_LAN”TStamp=“...”/> <MacInfo MAC=“00:20:a6:4c:bb:ad” RSSI=“7” Channels=“10”SSID=“EXPER” TStamp=“...”/> </Real-APs> <Disconnected-ClientsTStamp=“...”> <MacInfo MAC=“00:40:96:33:34:3e” RSSI=“57” Channels=“2048”SSID=“SOS_764” TStamp=“...”/> </Disconnected-Clients> </DiagPacket>

As the sample message shows, the DC sends information about otherconnected clients, APs, and disconnected clients. For each such class ofentities, it sends the MAC address of a machine along with RSSI, SSID,and a channel bitmap which indicates the channels on which theparticular device was overheard.

In view of the many possible embodiments to which the principles of thepresent invention may be applied, it should be recognized that theembodiments described herein with respect to the drawing figures aremeant to be illustrative only and should not be taken as limiting thescope of the invention. For example, those of skill in the art willrecognize that the illustrated embodiments can be modified inarrangement and detail without departing from the spirit of theinvention. Although the invention is described in terms of softwaremodules or components, those skilled in the art will recognize that suchmay be equivalently replaced by hardware components. Therefore, theinvention as described herein contemplates all such embodiments as maycome within the scope of the following claims and equivalents thereof.

1. A method for a first wireless client to indicate that it is unable toconnect to an infrastructure network, the method comprising actsperformed by the first wireless client of: attempting to connect to theinfrastructure network; determining that it is unable to connect to theinfrastructure network; and broadcasting, in response to determiningthat it is unable to connect to the infrastructure network, a signalindicating that it is unable to connect to the infrastructure network.2. The method of claim 1, wherein the act of determining that the firstclient is unable to connect to the infrastructure network furthercomprises an act of determining that it is unable to connect to theinfrastructure network by failing to receive any beacon signalstransmitted from an access point.
 3. The method of claim 1, wherein theact of determining that the first client is unable to connect to theinfrastructure network further comprises an act of determining that itis unable to connect to the infrastructure network by failing to receiveany probe response signals transmitted from an access point in responseto a probe request signal transmitted by the first client.
 4. The methodof claim 1, wherein the act of broadcasting a signal indicating that thefirst client is unable to connect to the infrastructure network furthercomprises an act of broadcasting a beacon signal indicating that thefirst client is unable to connect to the infrastructure network.
 5. Themethod of claim 1, wherein the infrastructure network operates accordingto the IEEE 802.11 protocol.